1. Field of the Invention
The present invention relates to an image binarization technique and, more particularly to an image processing technique for binarizing an image scanned by a shuttle type scanner in a multifunctional machine using a small amount of memory.
2. Description of the Related Art
Conventionally, a multifunctional machine is equipped with a scanner, a printer, a modem, a computer, etc. The multifunctional machine prints data scanned by the scanner or data transmitted from another system through the modem using the printer, or stores the data in a hard disk of the computer. The multifunctional machine is manufactured to perform the functions of a facsimile machine, printer, scanner and a copying machine.
There are two types of multifunctional machines, i.e., a shuttle type and an array type. The array type which supports a rapid scanning of a document is high in price. On the contrary, the shuttle type scans the document slower than the array type. However, since the shuttle type is low in cost, it has widely been used.
The scanning operation of a shuttle type scanner is explained below.
First, a part of the document is scanned by the scanner of the multifunctional machine. The unit scanned by the scanner is called a slice.
The size of the slice is decided by the number of pixels which are scanned at a time according to the number of charged coupled devices (CCDs) mounted on the scanner. For example, assuming that the number of CCDs of the scanner is 160 pixels in the longitudinal direction and the number of CCDs is 1 in the horizontal direction, then the size of the slice is 160.times.1.
Scanning the document is performed by moving the scanner from the most left edge of the document to the most right edge of the document per unit of slice. The scanner performs scanning by dividing the document per unit of band. The band indicates the amount of data of the document which is scanned once in the horizontal direction by the scanner.
In order to transmit data contained in the document through the facsimile machine after scanning the document, the scanned document is changed to data values of 0 or 1. Generally, the data scanned by the scanner is a gray color and has 256 values, i.e., 0 to 255. The values are expressed by 8 bits and the process for changing the values into binary values is called a binarization.
The binarization process includes two different methods, namely, an error diffusion method (EDF) and a threshold value method. Since these methods are well known to persons skilled in the art, a detailed description thereof has been omitted.
The binarization process according to the EDF method using a mask having 3.times.3 pixels in a shuttle type scanner is explained below.
In order to binarize one target pixel of data which has been scanned, the data binarization is performed by diffusing an error value generated when binarizing 1 pixel to 8 pixels neighboring the target pixel around the target pixel according to the weight of each mask cell. The aforesaid technique is called data binarization by the EDF method.
Generally, in the case of performing the binarization, since it is necessary to know the values of neighboring pixels before performing the EDF operation, scanned first band data and second band data containing an S region are stored and controlled. In addition, by substituting the value of a P region with a neighboring pixel value according to the principle of image processing, the image processing is performed by constituting the 3.times.3 mask.
Since the binarization method needs to have a band memory for storing and controlling the scanned document per unit of band for image-processing the pixel of the scanned document, it causes an increase in the cost of the multifunctional machine.
In addition, in the case of using a 3.times.3 mask for one band, since no data is contained in the end part of the band and in the beginning part of the next band, a boundary between the two bands is formed.